Our major aim is to understand the changes in nuclei of aneuploid CNS neoplasms. Isolation and characterization of subsets of repeated sequences in mouse and human DNA will be continued, with emphasis on chromosomal structure (studies by in-situ hybridization) and DNA analysis. Ultrastructural studies of the nucleolus organizing regions in interphase nuclei will be correlated with quantitative analysis of DNA restriction profiles from normal and neuroectodermal tumor cells, using defined ribosomal DNA probes. Methods to analyze other DNA sequence subsets of interest, with respect to their three-dimensional arrangement in chromosomes are currently being investigated.